It will be understood that efficient operation of engines such as gas turbine engines used for aircraft propulsion is important in terms of economy of operation as well as with respect to engine durability. In such circumstances, it is increasingly common to utilise relatively accurate sensing mechanisms in terms of monitoring engine performance for display to a user, as well as for utilisation within automatic control loops. Unfortunately, inherent thermal as well as mechanical variations between start up or other transients to steady state operation can be difficult to accommodate within these control regimes or may appear temporarily alarming to a user.
Of particular concern with respect to the present engine control is a situation with regard to fuel flow into a turbine engine during initial engine start up and rapid acceleration. It will be understood that an engine is generally cold at start up and therefore a proportion of the fuel flow, rather than being directed towards thrust or other prime movement is utilised in order to heat the engine components. This is known as “heat soak” within the engine and is generally accommodated by initial provision of additional fuel or a choke mechanism. This additional fuel, as indicated, acts to compensate for the heat soak effect of warming the engine components, but as the engine warms up it will be understood that there may be too much fuel flow and therefore effectively the engine is generating more than 100% of its rated performance. Thus, additional fuel is being used when not required and secondly through more accurate displays an alarming indication of such factors as turbine rotational speed as 2 or 3% above that acceptable may be displayed to users for a few seconds. This at least may cause anxiety and possibly lead to interactive compensation by the user.